[WS-2839]: Hide articles in myNews page when metadata is not present

[LukasFrm]

Resolves JIRA: https://bbc.atlassian.net/browse/WS-2839

Summary

Articles with metaData: null are now filtered out before rendering on the My News page.
Sanitises promoImageAltText before it is posted to the UAS favourites API. Article alt text containing newline characters (e.g. "शाहरुख़ ख़ान\n") was causing the stored metadata to be silently dropped when fetching saved articles back from UAS.

Code changes

• metaData made optional on UasActivityItem; items without it are filtered in getRecentActivity
• Add sanitiseMetadataString helper in uasUtility.ts that strips \r/\n characters and trims whitespace from a string before it is sent to UAS (otherwise if present inmetaData, the object itself is stripped).
• Apply sanitiseMetadataString to promoImageAltText so all save/update payloads are clean.
• Add a new uasUtility.test.ts with unit tests covering trailing newlines, \r\n, embedded newlines, empty/undefined input, and clean strings.

Testing

1. Save an article where the image alt text contains a trailing newline (POST payload's metaData should include promoImageAltText: "शाहरुख़ ख़ान\n" ).
2. Confirm the POST payload's metaData.promoImageAltText has no \n in it (check Network tab or logs).
3. Fetch saved articles (My News page) and confirm the article appears with correct metadata.
4. Run yarn test src/app/lib/uasApi/uasUtility.test.ts — all tests should pass.

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[elvinasv]

Tested using http://localhost.bbc.com:7081/hindi/articles/cwy0pz7qydzo?renderer_env=live(which has an invalid metadata). Works as expected 👍